The present invention relates to an implantable prosthesis for replacing a human hip or knee joint and the adjoining bone sections, wherein the prosthesis comprises a joint replacement part, a shaft replacement part being connectable to the joint replacement part or integral therewith and having a central cavity, as well as a rod-shaped shaft anchoring part being insertable into the cavity. An implantable prosthesis of this kind is known from EP 1 371 346 B1.
After resection of a bone tumor, the removed bone and the joint concerned can be replaced by a tumor prosthesis, and there is initially no difference in leg length. The prosthesis is anchored in the remaining bone, as described, for example, in EP 1 371 346 B1. When a difference in leg length develops due to growth, the bone can be osteotomized and the prosthesis can be provided with a distraction medullary nail instead of the shaft anchoring part for performing the callus distraction method. Distraction medullary nails of this kind are described, for example, in EP 0 432 253 B1.
If a second lengthening step is required, this procedure must be performed again. In any case, however, after completion of length growth, the distraction medullary nail, which cannot remain in place for permanent shaft anchoring, must be replaced by a stable shaft anchoring part. Exchange of a distraction medullary nail or replacement by a stable shaft anchoring part is often only possible if the joint components are decoupled, so that extensive operative exposure is required. Thus, in addition to resection of the tumor, at least two, in most cases even three extensive surgical operations are required near the joint in the region of the prothesis, which implies a considerable risk of infection.
Therefore the object underlying the invention is to considerably reduce the extent of a repeated surgical operation, and thus the risk of infection, in the case of a set tumor prosthesis while maintaining the advantages of bone lengthening according to the callus distraction method, wherein the artificial joint itself is to be touched as little as possible.